Method of making bifocal lenses comprising treating a preselected area of a single focal length lens with ionizing radiation

ABSTRACT

A method for obtaining corrective glass lenses which are provided with at least two zones having different powers so that one zone serves to view nearby objects and the other Zone serves to view distant objects wherein, in order to carry out a modification of power in a predetermined region of a corrective lens without entailing any alteration in the shape of said lens, said region is exposed to a radiation flux which results in a modification of its refractive index.

United States Patent Inventor Philippe Sinai 1 12, qua! Louis Bleriot,75 Paris l6erne. France AppL No. 1,864 Filed Jan. 9, 1970 Patented Oct.5, 1971 Priority Jan. 15, 1969 France 6,900,594

METHOD OF MAKING BIFOCAL LENSES COMPRISING TREATING A PRESELECTED AREAOF A SINGLE FOCAL LENGTH LENS WITH IONIZING RADIATION 22 Claims, 2Drawing Figs.

US. Cl 1 250/495 TE, 250/495 T, 350/175 GN, 350/178, 350/194, 351/169lltt.. r G021! 3/10, GOZc 7/06 Fieldol Search 250/495 TE, 49.5 GC, 49.5R, 106 R, 49.5 TC, 65/30 [56] References Cited UNITED STATES PATENTS3,486,808 12/1969 Hamblen 351/177 OTHER REFERENCES Optical WaveguidesFormed by Proton Irradiation of Fused Silica. Schineller, Journal of TheOptical Society of America, V01. 58, No. 9 Sept. 1968, pp 1171- 1176.

Primary Examiner-James W. Lawrence Assistant Examiner-C. E. ChurchAttorney-Craig. Antonelli & Hill HGI INVENTOR PHILIPPE SINAI us- AMkamsl- ATTORNEYS METHOD OF MAKING BIFOCAL LENSES COMPRISING TREATING APRESELECTED AREA OF A SINGLE FOCAL LENGTH LENS WITH IONIZING RADIATIONThe present invention relates to a method for obtaining corrective glasslenses which are provided with at least two zones having differentpowers, such lenses being adapted both to viewing of nearby objects aswell as objects located at optical infinity. The invention is alsoconcerned with the lenses obtained in accordance with said method. Glasslenses of this type which are well known in spectacle lens optics existat the present time either in the form of "bifocal lenses" or in theform of progressive curvature lenses," otherwise known simply as"progressive lenses."

In the majority of cases, a bifocal lens is intended for viewing objectslocated at optical infinity, a second lens having smaller dimensions andformed of a material having a different refractive index so as to permitviewing of nearby objects being added to the first lens in a zone whichis located offcenter. This zone can also be formed by grinding. Abifocal lens thus has two perfectly defined zones having separate anddistinct magnifying powers which are markedly different from each other.In consequence, wearers of spectacles which are fitted with lenses ofthis type not infrequently experience difficulty in becoming accustomedto them and only then after a long time.

A progressive lens also has a zone for viewing distant objects and azone for viewing nearby objects but these two zones which have differentpowers or so-called stabilized vision zones are separated in this caseby a third zone whose power progresses continuously from the near visionzone to the far vision zone. Thus, the eye can shift imperceptibly andtherefore without fatigue from distant vision accommodation to nearvision accommodation and conversely. This continuous power variation isobtained at the present time by means of a continuous variation in theradius of curvature of the glass. These lenses are fabricated either bymolding or by grinding.

It can readily be understood that the manufacture of bifocal lenses andof progressive lenses is particularly difficult and entails high capitalcost.

The precise aim of this invention is to propose a method for obtaininglenses of the type referred to above which makes profitable use of thevariations in refractive index produced in an optical medium bycorpuscular and electromagnetic radiatlons.

More precisely, the present invention is directed to a method ofobtaining corrective glass lenses which are provided with at least twozones having different powers so that one zone serves to view nearbyobjects while the other zone serves to view distant objects, said methodbeing mainly characterized in that, in order to carry out a modificationof power in a predetermined region of a corrective lens without therebyentailing any alteration in the shape of said lens, said region isexposed to a radiation flux which results in a modification of itsrefractive index.

Further properties of this invention will be brought out by thefollowing description and reference to the accompanying drawing whichgives by way of explanation but not in any limiting sense a number ofdifferent modes of operation which may be adopted in order to produce abifocal glass lens and a progressive lens by means of exposure toradiation.

The illustration of the invention can be made with the aid of the twoattached figures, wherein:

FIG. 1 shows a glass with double the normal focus, which comprises azone A for viewing distant objects and a zone B for viewing objectsclose up, and

FIG. 2 illustrates a progressive glass which comprises a zone A forviewing distant objects, a zone B for viewing closeup ob jects and anintermediate zone I assuring the transition between these two zones.

A bifocal corrective lens can be obtained in accordance with theinvention in a number of different ways. The starting element can be abifocal lens which is fabricated by the mechanical means at presentemployed and the power of either of its two zones can be modified bysubjecting the lens to a radiation flux of constant intensity.

In FIG. I, a double glass already having zones A and B obtained bycutting is shown one or even both of these zones is irradiated so as tomodify the indices of refraction thereof. An alternative method would beto provide a glass having only one refractive power region and inducethe second zone B by irradiation. The effect of this irradiation is tomodify the refractive index of the zone concerned and therefore thepower of that zone.

Starting from a single configuration of lens which has initially twowell-defined power zones, it is thus possible to obtain a whole seriesof lenses having different characteristics. The number of types oflenses to be produced by mechanical means is therefore considerablyreduced and this represents a substantial advantage from the economicstandpoint when the cost of manufacture of glass lenses of this type istaken into consideration.

Another mode of operation in accordance with the invention consists inemploying in this instance a normal lens, that is to say a lens having asingle optical center for viewing distant objects and in producing byirradiation the zone which is intended for viewing close objects.

To carry out this method one employs a glass with double the normalfocus (as shown in FIG. I) and produces therein, by irradiation, anintermediate zone I (as shown in FIG. 2); the zones A and B may, ofcourse, also be irradiated. Further, one may provide a progressive glasslens already cut, and irradiate one of the zones A and B, at the sametime as irradiating the zone I, so as to adapt it to the new indices ofA and B, or start with a normal glass lens with a single focus andproduce therein the zones 8 and I by irradiation.

Thus, there are a number of methods for fabricating a progressive lensin accordance with the invention. One method consists in employing aglass element in which the two zones for viewing nearby objects and forviewing distant objects have been produced in any desired manner. Inthis case. the glass element is exposed in the intermediate zone to aradiation flux having a continuously varying intensity in order toproduce a continuous variation of the refractive index in said element,thereby creating a zone having a power which progreses also in acontinuous manner when moving away from the near vision zone towards thedistant vision zone.

It will be apparent that modifications in the power of the twostabilized vision zones can be carried out conjointly by irradiationwith a flux of constant intensity which makes it possible as in the caseof bifocal lenses to reduce the number of types of glass to befabricated by mechanical means.

It is also possible to employ a stating element a progressive glass lenswhich is produced by the usual methods and then to modify by irradiationthe power of either of the two stabilized vision zones at the same timeas the power of the progressive power zone in order to adapt this powerto the new characteristics of the glass lens.

Finally, it is possible as in the case of bifocal lenses to employ asstarting element a normal lens which has a single optical center and toform by irradiation both the near vision zone and the intermediateprogressive power zone.

The glasses which have been treated can be either mineral glasses ororganic glasses. In the case of mineral glasses. irradiation is carriedout by means of a neutron flux whereas in the case of organic glasses,recourse is bad to gamma radiation or electrons.

One type of mineral glass which is particularly well suited to theabove-mentioned neutron irradiation treatment is a silicabase glasscontaining a low percentage (3 percent) of boron-l0 in the form of boricanhydride (8,0,) or lithium-6 in the form of lithium oxide Li0,). Itwill naturally be understood that any material can be employed oncondition that it does not contain any impurities which would be liableto exhibit any residual radioactivity after exposure to neutronradiation as this would incompatible with the high-radiation sensitivityof the human eye.

Variation in radiation flux intensity is obtained by means of a screenformed of a radiation-absorbing material, the thickness of which variesin such a manner as to obtain the desired law. When the irradiation iscarried out with electrons, the law of variation of the flux can beobtained by means of deflection under the action of an electric ormagnetic field.

In the majority of cases, the irradiated glasses are subjected to athermal decolorizing treatment at a temperature which is lower than thatof index recovery. This heat treatment can be accompanied by irradiationwith ultraviolet rays which has the effect of accelerating the removalof coloring. in some cases, the glasses are subjected to a complementarypolishing treatment for the purpose of correcting any variations involume which may have taken place during irradiation.

Finally, at the time of irradiation of glasses, additional indexmodifications can certainly be made in order to correct theseaberrations and their effects on the eye. The method employed is of thetype described in French Pat. No. PV I75 O43 filed on Nov. 22, 1968 inthe name of the present applicant.

It must be understood that this invention is not limited solely to theexamples hereinabove described and that the scope of this patent alsoextends to alternative forms of either all or part of the arrangementsherein described which remain within the scope of equivalent means aswell as to any application of such arrangements.

What I claim is:

l. A method for obtaining corrective glass lenses which are providedwith at least two zones having different powers so that one zone servesto view nearby objects and the other zone serves to view distantobjects, in order to carry out a modification of power in apredetermined region of a corrective lens without entailing anyalteration in the shape of said lens, comprising the step of modifyingthe refractive index of said region by exposing said region to aradiation flux.

2. A method in accordance with claim l for obtaining bifocal lensesprovided with only two zones having different powers, wherein saidmethod further comprises the step of irradiating at least one of saidzones with a radiation flux of constant intensity in space.

3. A method in accordance with claim 1 for obtaining progressive lensesor lenses in which said region lies between the zones having differentpowers and comprises a transition zone which exhibits the continuouslyvariable power, wherein said step of exposing said region to radiationflux comprises the step of irradiating said transition zone with aradiation flux whose intensity varies continuously in space.

4. A method in accordance with claim I for obtaining progressive lensesin which said region lies between the zones having different powers andcomprises a transition zone which exhibits a continuously variablepower, wherein said method comprises the steps of irradiating saidtransition zone with a radiation flux whose intensity variescontinuously in space and irradiating at least one of the two otherzones with a radiation flux whose intensity is constant in space.

5. A method in accordance with claim 1, wherein said corrective glass ismineral glass and wherein said irradiation steps comprise bombardingsaid mineral glass with neutrons.

6. A method in accordance with claim 1, wherein said glass is organicglass and said step of exposing said region to radiation flux comprisesbombarding said glass with gamma rays.

7. A method in accordance with claim l, further including the step ofsubjecting said glass to a thermal decolorizing treatment.

8. A method in accordance with claim I, further including the step ofsubjecting said glass to a polishing treatment after irradiation inorder to correct variations in volume which result from saidirradiation.

9. A method in accordance with claim 1 wherein said glass is organicglass and said step of exposing said region to radiation flux comprisesbombarding said glass with electrons.

10. A method in accordance with claim 2, further including the step ofsubjecting said glass to a thermal decolorization treatment.

II. A method in accordance with claim 3, further including the step ofsubjecting said glass to a thermal decolorization treatment.

12. A method according to claim 4, further including the step ofsubjecting said glass to a thermal decolorization treatment.

[3. A method according to claim 2, further including the step ofsubjecting said glass to a polishing treatment after irradiation inorder to correct variations in volume which result from saidirradiation.

14. A method according to claim 3, further including the step ofsubjecting said glass to a polishing treatment after irradiation inorder to correct variations in volume which result from saidirradiation.

15. A method in accordance with claim 4, further including the step ofsubjecting said glass to a polishing treatment after irradiation inorder to correct variations in volume which result from saidirradiation.

16. A method of obtaining a corrective glass lens comprising the stepsof:

providing a glass lens having two zones of diflerent powers, one zoneserving for viewing nearby objects. while the other zone serves forviewing distant objects; and

modifying the refractive index of a predetermined region of said lens byexposing said lens to a radiation flux,

whereby the power of said predetennined region will be altered withoutchanging the shape of said lens.

17. A method according to claim 16, wherein said step of providing aglass lens having two zones of different powers comprises the step ofirradiating a first zone of a glass lens with flux of constantintensity.

18. A method according to claim 17, wherein said step of modifying therefractive index of a predetermined region of said lens includes thestep of exposing said region to a flux of radiation, the intensity ofwhich varies in space.

19. A method according to claim l8, wherein said step of providing saidglass lens comprises providing a silica-base glass having asubstantially small percentage of boronl 0.

20. A method according to claim 18, wherein said step of providing saidglass lens comprises providing a silica-base glass having asubstantially small percentage of lithium-6.

2!. A method according to claim 19, wherein said silicabase glasscontains boric anhydride.

22. A method according to claim 20, wherein said silicabase glasscontains lithium oxide.

1. A method for obtaining corrective glass lenses which are providedwith at least two zones having different powers so that one zone servesto view nearby objects and the other zone serves to view distantobjects, in order to carry out a modification of power in apredetermined region of a corrective lens without entailing anyalteration in the shape of said lens, comprising the step of modifyingthe refractive index of said region by exposing said region to aradiation flux.
 2. A method in accordance with claim 1 for obtainingbifocal lenses provided with only two zones having different powers,wherein said method further comprises the step of irradiating at leastone of said zones with a radiation flux of constant intensity in space.3. A method in accordance with claim 1 for obtaining progressive lensesor lenses in which said region lies between the zones having differentpowers and comprises a transition zone which exHibits the continuouslyvariable power, wherein said step of exposing said region to radiationflux comprises the step of irradiating said transition zone with aradiation flux whose intensity varies continuously in space.
 4. A methodin accordance with claim 1 for obtaining progressive lenses in whichsaid region lies between the zones having different powers and comprisesa transition zone which exhibits a continuously variable power, whereinsaid method comprises the steps of irradiating said transition zone witha radiation flux whose intensity varies continuously in space andirradiating at least one of the two other zones with a radiation fluxwhose intensity is constant in space.
 5. A method in accordance withclaim 1, wherein said corrective glass is mineral glass and wherein saidirradiation steps comprise bombarding said mineral glass with neutrons.6. A method in accordance with claim 1, wherein said glass is organicglass and said step of exposing said region to radiation flux comprisesbombarding said glass with gamma rays.
 7. A method in accordance withclaim 1, further including the step of subjecting said glass to athermal decolorizing treatment.
 8. A method in accordance with claim 1,further including the step of subjecting said glass to a polishingtreatment after irradiation in order to correct variations in volumewhich result from said irradiation.
 9. A method in accordance with claim1 wherein said glass is organic glass and said step of exposing saidregion to radiation flux comprises bombarding said glass with electrons.10. A method in accordance with claim 2, further including the step ofsubjecting said glass to a thermal decolorization treatment.
 11. Amethod in accordance with claim 3, further including the step ofsubjecting said glass to a thermal decolorization treatment.
 12. Amethod according to claim 4, further including the step of subjectingsaid glass to a thermal decolorization treatment.
 13. A method accordingto claim 2, further including the step of subjecting said glass to apolishing treatment after irradiation in order to correct variations involume which result from said irradiation.
 14. A method according toclaim 3, further including the step of subjecting said glass to apolishing treatment after irradiation in order to correct variations involume which result from said irradiation.
 15. A method in accordancewith claim 4, further including the step of subjecting said glass to apolishing treatment after irradiation in order to correct variations involume which result from said irradiation.
 16. A method of obtaining acorrective glass lens comprising the steps of: providing a glass lenshaving two zones of different powers, one zone serving for viewingnearby objects, while the other zone serves for viewing distant objects;and modifying the refractive index of a predetermined region of saidlens by exposing said lens to a radiation flux, whereby the power ofsaid predetermined region will be altered without changing the shape ofsaid lens.
 17. A method according to claim 16, wherein said step ofproviding a glass lens having two zones of different powers comprisesthe step of irradiating a first zone of a glass lens with flux ofconstant intensity.
 18. A method according to claim 17, wherein saidstep of modifying the refractive index of a predetermined region of saidlens includes the step of exposing said region to a flux of radiation,the intensity of which varies in space.
 19. A method according to claim18, wherein said step of providing said glass lens comprises providing asilica-base glass having a substantially small percentage of boron-10.20. A method according to claim 18, wherein said step of providing saidglass lens comprises providing a silica-base glass having asubstantially small percentage of lithium-6.
 21. A method according toclaim 19, wherein said silica-base glass contains boric anhydride.
 22. Amethod accordiNg to claim 20, wherein said silica-base glass containslithium oxide.